I was curious about this and did some further testing … Do note that your code doesn’t simply reverse the prompt — it reverses it and also puts spaces between the characters 
See screenshot below for the difference in how it works (at least as per the screenshots you shared …)
So, I decided to try both versions of the negative prompt and see what happened with each … Here’s the three resulting images …
I can’t tell which one is more detailed, but my wife who has a better eye than I, says that image 2 (the one with the spaces between each letter) is the one which is the most detailed … I just have no idea why